There are various alloys developed for special applications including, for example, die casting of automotive components. Among these alloys magnesium-aluminium alloys can be designated as cost-effective and widely used for manufacture of automotive parts, e.g. AM50A alloy (where AM means aluminium and manganese are in the components of the alloy) containing approx. 5 to 6 wt. % aluminium and manganese traces, and magnesium-aluminium-zinc alloys, e.g. AZ91D (where AZ means aluminium and zinc are in the components of the alloy) containing approx. 9 wt. % aluminium and 1 wt. % zinc.
The disadvantage of these alloys is their low strength and poor creep resistance at elevated operating temperatures. As a results, the above mentioned magnesium alloys are less suitable for motor engines where some components such as transmission cases are exposed to temperatures up to 150° C. Poor creep resistance of these components can lead to a decrease in fastener clamp load in bolted joints and, hence, to oil leakage.
Known is a magnesium-based alloy (PCT/CA96/00091) comprising aluminium and calcium as alloying components in the following contents:    Aluminium—2–6 wt. %    Calcium—0.1–0.8 wt. %    Magnesium—rest being
As a drawback of the above alloy it can be noted that alloys having higher calcium content are prone to hot cracking in die casting.
Known presently is another magnesium die cast alloy (U.S. Pat. No. 5,855,697) which is taken as analogue-prototype and comprises magnesium, aluminium, zinc, and calcium as the basic alloying components in the following contents:    Aluminium—2–9 wt. %    Zinc—6–12 wt. %    Calcium—0.1–2.0 wt. %.
The alloy can also comprise other ingredients such as manganese in the amount of 0.2 to 0.5%, silicon up to 0.05% and impurities, e.g. iron in the amount of 0.01 to 0.008 wt. %.
Table 1 of the prototype patent discloses the composition of the alloys ZAC8502, ZAC8506 and ZAC8512 that comprise the components in the following contents, wt. %: 4.57–4.67 aluminium, 8.12–8.15 zinc, 0.23–1.17 calcium and 0.25–0.27 manganese. The alloy of the above composition was subjected to mechanical tests and compared to conventional alloys AZ91 and AE42 in relation to their mechanical properties. This alloy contains magnesium, aluminium, zinc and calcium as the basic alloying components whereas silicon is included in the alloy as an impurity in the amount up to 0.05% which is therefore considered to be a shortcoming of the alloy. Addition of aluminium, zinc and calcium results in the formation of intermetallic precipitates Mg—Al—Zn—Ca along grain boundaries in primary magnesium. The microstructure obtained in this alloy is characterised with a larger grain size and leads to lack of structure homogeneity which is detrimental to mechanical properties of the alloy in die-casting processes.
Presently known is the method (PCT Patent No. 94/09168) for producing a magnesium-based alloy that provides for alloying components in a molten state being introduced into molten magnesium. Primary magnesium and alloying components are therefore heated and melted in separate crucibles. Elemental manganese is alloyed here with other alloying metals before they are added in molten magnesium to increase efficiency of melt refining from iron inclusions.
What is disadvantageous of this method is the need to pre-melt manganese and other alloying elements (at the melting temperature of 1250° C.) that complicates alloy production and process instrumentation.
There are some other methods known (B. I. Bondarev “Melting and Casting of Wrought Magnesium Alloys” edited by Metallurgy Publishing House, Moscow, Russia 1973, pp 119–122) to introduce alloying elements using a master alloy, e.g. a magnesium-manganese master alloy (at the alloying temperature of 740–760° C.).
This method is disadvantageous because the alloying temperature should be kept high enough which leads to extremely high electric power consumption for metal heating and significant melting loss.
Also known is another method of producing a magnesium-aluminium-zinc-manganese alloy (I. P. Vyatkin, V. A. Kechin, S. V. Mushkov in “Primary magnesium refining and melting” edited by Metallurgy Publishing House, Moscow, Russia 1974, pp. 54–56, pp. 82–93) which is taken as an analogue-prototype. This method stipulates various ways how to feed molten magnesium, alloying components such as aluminium, zinc, manganese. One of these approaches includes simultaneous charging of solid aluminium and zinc into a crucible, then heating above 100° C., pouring in molten magnesium and again heating up to 700–710° C. and introducing titanium-containing fusion cake together and manganese metal under continuous agitation.
The main shortcoming of the method is in considerable loss of alloying components resulting in lower recovery of alloying components in magnesium and preventing from producing alloys of the specified quality. Said quantitative composition of the magnesium-based alloy is able to improve mechanical properties.